Process for spinning polyvinyl alcohol filaments and remaining impurities therefrom



Aug. 1961 G. M. MOELTER ETAL 2,994,575

PROCESS FOR SPINNING POLYVINYL ALCQHOL FILAMENTS AND REMAINING IMPURITIES THEREFROM Filed Sept. 9. 1954 I II 11/11/11 11! \GGOOQOQO IN V EN TOR. Gnseoxv M Moan-K JESSE I. RILEY A 77'OP/YEYS United States Patent f PROCESS FOR SPINNING 'POLYVINYL ALCOHOL FILAMENTS AND REMAINING IMPURITIES THEREFROM Gregory M. lVIoelter, Basking Ridge, and Jesse L. Riley,

New Providence, NJ., assignors to Celanese Corporatron of America, New York, N.Y., a corporation of Delaware Filed Sept. 9, 1954, Ser. No. 455,019 -4 'Claims. (31. 18-54) This invention relates to the production of filamentary material and relates more particularly to the production of water-soluble filamentary material from polyvinyl al cohol.

It is an object of this invention to provide a novel, efiicient and economical process for the production of water-soluble filamentary material from polyvinyl alcohol.

It is a further object of this invention to provide a new and efiicient process for the production of filaments of polyvinyl alcohol by spinning an aqueous solution of polyvinyl alcohol into an aqueous salt solution.

In accordance with one aspect of this invention a yarn is produced by spinning a water solution of polyvinyl alcohol into a coagulating bath, or spin bath, comprising an aqueous solution of a salt having substantially no oxidizing action, preferably sodium sulfate. The wet yarn containing a considerable proportion of the salt is then treated with acetone which extracts the water from the yarn and aids in the removal of most of the salt. Advantageously the water-swollen coagulated yarn is stretched to increase its tenacity before it is treated with the acetone. The resulting treated yarn is strong and water-soluble.

The invention may be more easily understood from a consideration of the accompanying drawing illustrating one embodiment of the invention, wherein:

.FIG. 1 is a cross-sectional view in elevation of that portion of the apparatus in which the polyvinyl alcohol yarn is spun and stretched,

FIG. 2 is a side view, on a larger scale than FIG. 1, of the snubbing frame shown in FIG. 1, which snubbing frame is employed for the stretching of the yarn, and

FIG. 3 is a side view of that portion of the apparatus in which the yarn is treated with acetone and then dried, lubricated and twisted.

Referring now to the drawing, and more particularly to FIG. 1 thereof, reference numeral 11 designates a vessel containing a spin bath 12 comprising an aqueous solution of a non-oxidizing salt, such as sodium sulfate, preferably a saturated solution thereof. Spent spin bath is withdrawn from one end of the vessel 11, through an overflow pipe 13, and fresh, or regenerated, spin bath is supplied at the other end thereof through a pipe 14. A spinneret 16 having a number of fine orifices is positioned in the spin bath 12 and is connected to a pipe 16 through which an aqueous solution of polyvinyl alcohol is supplied under pressure.

The polyvinyl alcohol solution emerges from the orifices of the spinneret 16 in the form of a number of fine filaments 18, which filaments travel through the spin bath to a guide 19 where they converge to form a yarn 21. From the guide 19 the yarn is passed around a pair of freely rotatable rubber-covered skew rolls 22 in a helical path. The rolls 22 are so arranged that the helix of yarn moves along the length of said rolls. The size and spacing of the rolls 22 and the number of spaced turns the yarn makes thereon are so adjusted, in relation to the speed of the yarn, that the filaments of said yarn remain in the spin bath 12 for a period of time suflicient to insure that the filaments are substantially completely coagulated. The term completely coagulated, as used herein, means that further immersion in the spin bath,

l atented Aug. 1, 1961 e.g. the aqueous saturated sodium sulfate solution, will result in substantially no further coagulation of the filaments. At this stage the entire polymer has precipitated, the amount of water present in the yarn being that which is in equilibrium with the spin bath.

-In order to increase the speed of coagulation the spin bath should be maintained at an elevated temperature, e.g. about 32 to 70 C. by any suitable means. It has also been found that the speed of coagulation may be increased materially by incorporating into the aqueous polyvinyl alcohol spinning solution a minor proportion of the same salt as is used in the spin bath. Thus, up to about 2% of sodium sulfate may be added to a spinning solution containing about 15 to 20% of polyvinyl alcohol. For example, in one procedure the spinning solution contains 17% of polyvinyl alcohol and 0.15% of sodium sulfate.

After leaving the rolls 22 the coagulated yarn, which is still swollen with water, emerges from the spin bath 12, passing under tension through a snubbing device 23, stationary guides 24 and 26, and a traversing guide 27, and is wound under tension on a driven bobbin 28, or other suitable yarn package support.

The rotation of the bobbin 28 serves to draw the filaments of the yarn from the spinneret 16, around the skew rolls 22 and through the snubbing device 23, and serves to stretch the filaments. A substantial amount of stretching, e.g. about 50 to 350%, takes place as the yarn passes through the snubbing device to the bobbin 28. stretching causes the polyvinyl alcohol in the yarn to become oriented in the direction of stretching and increases the tenacity of the yarn, as is well known in the art. However, when the yarn is stretched too much, e.g. to such an extent that the tenacity of the yarn, after drying, is appreciably greater than 3 grams per denier,

the water solubility of the yarn is decreased.

The amount of stretching or draw-down which takes place in the spin bath 12 before the yarn is substantially fully coagulated is advantageously low. When the polyvinyl alcohol yarn is highly stretched in the spin bath before it is fully coagulated, its physical properties (i.e. tenacity and elongation at break) are not as good, even after further stretching of the fully coagulated yarn, as those of a yarn which has not been highly stretched before full coagulation.

The snubbing device 23 is composed of a frame 29 having a plurality of parallel pins 31 projecting horizontally therefrom. The yarn is threaded between the pins 31 in the manner shown generally in FIG. 1 so that the yarn is forced, by the tension on said yarn, against the surfaces of said pins. As shown in FIG. 2 the pins 31 are arranged in such a manner that, as the yarn proceeds upwardly through the snubbing device 23, the snubbing action of the pins 31 on the yarn will increase, i.e. a greater length of yarn will be forced into contact with each successive pin. More particularly, the pins at the top of the snubbing device overlap the vertical general line of travel of the yarn to a greater extent than the pins at the bottom of said snubbing device. It will be apparent that the tension on the yarn increases progressively as the yarn passes from the bottom pin to the top pin. The tension in the yarn, and therefore the extent to which the yarn is stretched, may be regulated by removing or adding pins 31 to the frame-29. The snubbing device 23 has the further function of removing entrained spin bath liquor'from the yarn.

It has been found that the best and most uniform results are obtained when the pins 31 have matte surfaces. Thus, when pins having polished, chromium plated surfaces are employed, the variations in yarn tension. are twice as great as when the same polished chromium plated pins are first sand blasted, as with sand grit, be-

This

fore use. Outstanding results are obtained when the pins are made of a ceramic material such as that known as Alsimag (a double silicate of aluminum and mag nesium sold by the American Lava Corporation, e.g. Alsimag #192), the surfaces of the pins being first sandblasted, as with #100 sand grit, and then vapor blasted with a finer grit, e.g. with #1600 grit silicon carbide abrasive in water. The subsequent blasting with the finer grit results in a substantial decrease in the number of breaks in filaments occurring during the process.

As stated, the yarn is preferably fully coagulated in the spin bath 11. The use of the rubber-covered rolls 22 has been found highly advantageous in enabling this full coagulation to 'be effected at a very rapid rate. Thus, when other types of rolls, such as rolls having hard plastic surfaces, e.g. phenol-formaldehyde resin surfaces, are employed the yarn tends to slip sidewise along the surfaces of the rolls. When attempts are made to overcome this difliculty by the use of grooved rolls, the filaments of the yarn tend to draw closely together in the grooves so that the spin bath does not come into free contact with all of said filaments and coagulation of the filaments in the interior of the yarn is delayed. In addition, in some instances the use of grooved rolls causes coalescence. of the filaments. In contrast, when the rubber-covered rolls are employed the yarn in contact with said rolls takes the form of a flat ribbon 'and the coagulation of all the filaments of the yarn is uniform. This is true even when the yarn passing over such rolls is under very low tension, which low tension is desirable in order to avoid undue stretching of the yarn before it has been fully coagulated. It is to be understood, of course, that the rubber employed for covering the rolls may be any suitable type and may be natural or synthetic rubber. Conveniently and economically, the rolls 22 may be constructed by applying sleeves made from vulcanized pure gum natural rubber tubing to rolls made of phenolformaldehyde resin. Such sleeves are easily replaceable when worn.

In the embodiment shown in FIG. 1 there is also provided an alternate driven bobbin, or other yarn package support, 32, together with an alternate traverse guide 33 and stationary guide 34. After the first bobbin 28 has been fully wound the 'yarn is broken and transferred, through the guides 33 and 34, to the second bobbin 32, the first bobbin 23 being then dolfed and replaced by an empty bobbin. 7

The bobbins 28 and 32 and the snubbing device 23 are enclosed within a cabinet 36 which is supported in any suitable manner with its bottom edge just above the level of the spin bath 12. A stream of steam is fed continuously to the interior of the cabinet by means of a pipe 37. In this manner the yarn leaving the spin bath 12 is maintained in a gaseous atmosphere of substantially 100% relative humidity in order to prevent the salt of the spin bath from crystallizing out on the yarn.

When, as is preferred, the spin bath 12 is a solution of sodium sulfate, this salt tends to dry out on the surface of the yarn in the form of relatively large crystals of anhydrous sodium sulfate. The presence of these crystals makes it difiicult to carry out textile operations, such as winding, unwinding, or twisting, without breaking the yarn. In accordance with one feature of this invention it has been found that if the yarn is dried at a temperature of less than 32.4 C. the salt crystallizes out in the form of sodium sulfate decahydrate which, on further drying at relatively low humidity and at a temperature below 324 C. loses water of crystallization to form anhydrous sodium sulfate in very fine form. Yarn carrying such fine particles has much less tendency to break when subjected to textile operations than yarn carrying the anhydrous sodium sulfate in the form of'large crystals. Accordingly, in an alternative form of the invention, less desirable than that shown in FIG. 1, the salt is allowed to dry on the bobbin during the winding operation while the air around the bobbin is maintained at a temperature below the transition temperature 32.4 C. and at a relatively low humidity. Since the air above the heated spin bath is generally hotter than 324 C., means, such as a fan directed at the bobbin, are provided for bringing cooler air into contact with the yarn on said bobbin. In this embodiment, it is also desirable to prevent the crystallization of the salt on the snubbing device or on the guides. To this end, drying of the salt at these points is avoided by continuously pouring a liquid, such as the spin bath liquor, over the snubbing device and guides by any suitable means.

In the preferred embodiment, after the bobbin 28 is fully wound it is removed from the cabinet 36 and placed in a container 41 (FIG. 3) where it is subjected to the action of an organic water-soluble liquid which is a nonsolvent for the salt carried by the yarn and a non-solvent for the polyvinyl alcohol. Acetone is the preferred organic liquid. The acetone is continuously supplied to the container 41 through an inlet 42 and discharged therefrom through an outlet 43 situated near the bottom of said container. The container is provided with a cover 44 to minimize evaporation of acetone therefrom. Near the top of the cover 44 there are provided friction means in the form of a series of snubbing pins 46 situated above the upper level of the acetone in the container 41. The yarn 21 is drawn off the end of the bobbin 28 and passes over the snubbing pins, through an aperture 47 in the cover 44, around a guide roll 48, past a drier 49 and an applicator 51 which coats the yarn with a lubricant therefor, to the driven feed roll 52 of a ring spinner 53, of conventional construction, wherein the yarn is twisted and wound on a driven bobbin 54, or other yarn package support.

The acetone serves to set the water-swollen yarn by extracting water therefrom and also acts to precipitate, in very fine particles, the salt carried by said water-swollen y-arn, which water-swollen yarn carries more than 5%, and sometimes more than 10%, by weight of salt and about 30 to 60% by weight of water, based on the weight of said water-swollen yarn. The precipitated salt is removed from the yarn mechanically by the whipping about of the balloon of yarn coming off the end of the bobbin 28 and by the rubbing of the yarn again the snubbing pins 46. The salt, which is insoluble in the acetone, sinks to the bottom of the container and is removed with the acetone through the outlet. By the use of this method the salt content of the yarn is reduced to about 2% or less, and the water content to about 4 to 6%, based on the weight of the yarn as conditioned at 50% relative humidity and 77 F.

The setting action of the acetone on the oriented waterswollen polyvinyl alcohol yarn takes place rapidly to produce a yarn which has substantially no tendency to shrink on drying. This particular property of acetone is not shared by other volatile solvents such as methanol, ethanol and methyl ethyl ketone. For example, when samples of oriented water-swollen polyvinyl alcohol yarn are immersed at constant length for 1 minute in acetone, methanol and ethanol, respectively, and then dried in an unstressed state in air at'25' C. and 40% relative humidity, the acetone-treated yarn shrinks only 12% while the methanoland ethanol-treated yarns shink 54% and 52%, respectively. When samples of the oriented water-swollen polyvinyl alcohol yarn are stretched 250% and immersed for 10 minutes in acetone and methanol, respectively, while holding said samples at constant length, and thereafter allowed to shrink freely in the solvent, the sample immersed in acetone shows no tendency to shrink (the shrinkage being 0.0%) while the sample immersed in methanol shrinks 9.7%.

Although the acetone acts quickly on the oriented water-swollen polyvinyl alcohol yarn, merely immersing a bobbin wound with said yarn intothe acetone is not efiective. This is due to the fact that the yarn is wound tightly around the bobbin, so that the acetone affects merely the outer layers of yarn on the bobbin. Even when the acetone is forced through the windings on the bobbin under superatmospheric pressure or with the aid of vacuum the treatment is relatively slow and effects the removal of only' a minor proportion of the salt. The method illustrated in FIG, 3, however, sets the yarn and removes most of the salt very conveniently, effectively and economically.

Advantageously, the acetone is in contact with the yarn for at least five minutes. In the preferred embodiment, the rate at which the yarn is withdrawn from the bobbin in the acetone bath is slow enough to permit all portions of the yarn to become substantially completely set, i.e. set to such an extent that the degree of shrinkage is 3% or less, preferably zero. The rate at which the yarn is withdrawn from the bobbin in the acetone bath is sulficiently slow so that the setting action of the acetone takes place primarily while the yarn is wound on the bobbin. Thus, the yarn is maintained substantially at constant length while it is being set by the acetone, being kept at such constant length by the windings.

The acetone passing through the container 41 absorbs water from the yarn. For best results, the water content of the acetone in contact with the yarn should be relatively low. Thus, the acetone should be passed through the container at such a rate that the concentration of water in the aqueous acetone leaving said container is not above about It will be understood, of course, that the acetone withdrawn from the container 41 through the outlet 43 may be treated to remove the salt and water therefrom, and may then be recycled to the inlet 42. For example, the salt may be removed by filtration or decantation and the water by distillation or by passing the acetone over a drying agent such as calcium chloride Due to the high volatility of the acetone it evaporates rapidly from the yarn passing from the container 41. For example, when the drier 49 is merely a small fan blowing air at room temperature over the yarn, the acetone is removed from the travelling yarn within a period of travel of less than 5 seconds. Of course, by the use of heat the drying may be greatly accelerated.

As stated previously, the fully wound bobbin 28 removed from the cabinet 36 (FIG. 1) is transferred to the container 41 (FIG. 3). It is desirable to prevent the yarn on this bobbin from drying out appreciably, particularly if the yarn contains sodium sulfate and is to be exposed to temperatures above the transition temperature of the sodium sulfate, i.e. 32.4 C., during such drying. Accordingly in one convenient procedure, if it is necessary to store the wound bobbin before it is transferred to the container 4-1, said bobbin is wrapped with a film of substantially moisture-impermeable material, such as polyethylene, which prevents drying during the storage period. In another, but less desirable, procedure the yarn on the bobbin is dried in air at a temperature not above the transition temperature of the sodium sulfate, i.e. 32.4 C., and the dried yarn is unwound, in the manner shown in FIG. 3, in the container 41, where it is subjected to the action of the acetone. Here the acetone does not effect any substantial dehydration of the yarn or the salt but its presence aids in the mechanical removal of the salt from the yarn without the formation of dust and without breakage of the filaments. In this case other organic liquids which are non-solvents for the polyvinyl alcohol and which are preferably volatile, e.g. methanol, ethyl acetate, or carbon tetrachloride, may be employed in place of the acetone.

The set yarn wound on the bobbin 54 (FIG. 3) tends to absorb moisture if the relative humidity is above about 50%. Hence, if this yarn is to be stored before use it should be maintained at a lower relative humidity. Here again, the bobbin of yarn may be wrapped in polyethylene or other film substantially impermeable to moisture during the storage period.

When the polyvinyl alcohol used for the preparation of the spinning solution employed in the process of this invention is one which has been subjected to drying at high temperatures, e.g. to 200 C., there is some tendency for the yarn produced from such spinning solution to have a slight yellow cast, particularly when the salt content of the yarn is low. In accordance with one aspect of this invention it has been found that the color-forming tendency may be removed by the addition of small amounts of hydrogen peroxide, e.g. in the form of a 3% aqueous solution thereof, to the spinning solution. An amount of hydrogen peroxide of about 4, of the weight of the polyvinyl alcohol is particularly effective. The color-forming tendency may also be eliminated by the addition of small amounts of sulfuric acid, e.g. amounts of /2% of the weight of the polyvinyl alcohol, to the spinning solution.

The following example is given to illustrate the invention further.

Example I A spinning solution is prepared containing 17% by weight of polyvinyl alcohol, 0.3% by weight of Penetronyx D-40, 1% by weight of isopropanol, 0.017% of hydrogen peroxide and the balance water. The polyvinyl alcohol is one produced by the alkaline hydrolysis of polyvinyl acetate, the degree of hydrolysis being 88.5% 10.8% and the intrinsic viscosity of the polyvinyl alcohol in water at 25 C. being 0.80:0.05. The Penetronyx D-40 is a wetting agent comprising dimethyl beta-hydroxyethyl lauryl ammonium chloride and serves to promote solution of the polyvinyl alcohol, to disperse any gels which may form, and to improve ease of the filtration of the solution. The isopropanol acts as an anti-foaming agent.

The spinning solution is filtered and then forced through the fine orifices of a spinneret into a. spin bath having a temperature of 50 C. and composed of a saturated aqueous solution of sodium sulfate. The resulting filaments of polyvinyl alcohol pass through the spin bath where they are fully coagulated, the residence time of said filaments in said bath being 50 seconds. The yarn composed of said coagulated filaments is then stretched by passing it under a tension through a snubbing device and the stretched yarn is wound up under tension on a driven bobbin, being stretched about 250% at a stretching tension of grams. During the stretching and winding operation the yarn is maintained in an atmosphere saturated with moisture at atmospheric pressure by the injection of steam into a cabinet surrounding said snubbing device and bobbin.

The fully Wound bobbin of yarn is then transferred directly to a bath of acetone where it is maintained for 15 minutes, following which the yarn is drawn off from the bobbin while the latter is still immersed in acetone, the yarn being taken over the end of the bobbin through a series of snubbing pins at the rate of 60 meters per minute and then dried, lubricated with a water soluble wetting agent, and given a twist of two turns per inch and wound up on a second bobbin on a ring spinner. During this process the acetone concentration in the bath is maintained at at least 95% by weight. The resulting yarn, having a denier of 210 and comprising 60 filaments, has a tenacity of 2.7 grams per denier, an elongation of 17 and a sodium sulfate content of 2%. The measurements of tenacity and elongation are made at a relative humidity of 50% and a temperature of 23 C.

The yarn is tested for Water-solubility by taping the ends of a small portion of the yarn to a glass microscope slide under tension, covering the yarn with a cover glass, and observing the yarn under a microscope while water at room temperature is run onto the yarn. The tests are carried out at two different yarn tensions, i.e.

7 0.25 and 0.75 gram per denier. It is found that after a few minutes, at each of said tensions, the structure of the yarn cannot be distinguished in the field of observation of the microscope, showing that theyarn is completely soluble in water.

While the use of sodium sulfate as the salt in the spin "bath yields optimum results in the practice of this invention other salts may be employed instead of, or in addition to the sodium sulfate.

scription is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

1. Process for the production of yarn from polyvinyl alcohol, Which comprises spinning an aqueous solution of polyvinyl alcohol into a spin bath comprising a concentrated saline solution to form a plurality of polyvinyl alcohol filaments, collecting said filaments into a yarn, withdrawing said yarn from said spin bath and placing said yarn under tension to stretch said yarn to increase its tenacity, the degree of stretching being such that said yarn remains water-soluble, winding the stretched yarn containing water and salt under tension on a yarn package support, said stretching and said winding being carried out in an atmosphere substantially saturated with water to prevent drying of said yarn, immersing the resulting wound yarn package support in acetone and drawing the yarn off said yarn package support during said immersion whereby to set said yarn and to precipitate said salt in the form of fine particles, bringing the acetone-wet yarn into frictional contact with a solid surface to remove said 8 fine particles therefrom, and evaporating as the acetone from said yarn.

2. Process as set forth in claim 1 in which said saline solution is a substantially saturated solution of sodium sulfate.

3. Process as set forth in claim 2 in which said solution of polyvinyl alcohol contains up to about 2%, based on the weight of said solution, of sodium sulfate and contains about 34 based on the weight of polyvinyl alcohol, of hydrogen peroxide.

4. Process for the production of filamentary material from polyvinyl alcohol, which comprises immersing a yarn package support wound with water-soluble Waterswollen polyvinyl alcohol yarn containing sodium sulfate into a bath of acetone, the acetone acting to precipitate said sodium sulfate in fine particles, unwinding said yarn from said support while said support is immersed in acetone, and bringing said yarn wet with acetone into frictional contact with a solid surface to remove wet particles of sodium sulfate therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,958,670 Lubberhuizen et al May 15, 1934 2,289,232 Babcock July 7, 1942 2,388,325 Houtz Nov. 6, 1945 2,393,595 Dawson Jan. 29, 1946 2,474,617 Cline June 28, 1949 2,558,733 Cresswell et al. "July 3, 1951 2,591,242 Drisch et al. Apr. 1, 1952 OTHER REFERENCES Ser. No. 343,168, Ichiro Sakurada et al. (A.P.C.), published Apr. 27, 1943. 

4. PROCESS FOR THE PRODUCTION OF FILAMENTARY MATERIAL FROM POLYVINYL ALCOHOL, WHICH COMPRISES IMMERSING A YARN PACKAGE SUPPORT WOUND WITH WATER-SOLUBLE WATERSWOLLEN POLYVINYL ALCOHOL YARN CONTAINING SODIUM SULFATE INTO A BATH OF ACETONE, THE ACETONE ACTING TO PRECIPITATE SAID SODIUM SULFATE IN FINE PARTICLES, UNWINDING SAID YARN FROM SAID SUPPORT WHILE SAID SUPPORT IS IMMERSED IN ACETONE, AND BRINGING SAID YARN WET WITH ACETONE INTO FRICTIONAL CONTACT WITH A SOLID SURFACE TO REMOVE WET PARTICLES OF SODIUM SULFATE THEREFROM. 